JPH055620B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of the Invention] The present invention is a method for monitoring tool breakage and abnormalities in machine tools using acoustic emission (hereinafter referred to as AE) that occurs during cutting and tool breakage.
This invention relates to a tool breakage detection device that automatically detects tool breakage.

[Summary of the invention]

The present invention has a mounting portion with a shape corresponding to a tool,
AE obtained at the same level as when broken and when broken
Pseudo that generates a pseudo AE signal that includes the frequency of the signal
An AE signal generating means is attached to the tool mounting position of the machine tool, and an AE sensor is provided on the tool support. By adjusting the AE sensor sensitivity using the pseudo AE signal generation means installed in this way, even if the tool breaks, the AE will be generated through the same transmission path as the pseudo AE signal.
Since the signal is transmitted, the sensitivity of the AE sensor can be adjusted reliably, resulting in a highly reliable tool breakage detection device.

[Prior art and its problems] When cutting an object to be machined (hereinafter referred to as a workpiece) using a tool on a machine tool, the tool may break for some reason or become clogged with chips, resulting in abnormal cutting. . With the recent progress in factory automation, there is a strong demand for automatic detection of tool breakage and abnormal cutting. As a method for detecting breakage of tools in machine tools, conventional methods have been to
A device has been proposed that includes an AE sensor and detects tool breakage based on the AE signal obtained from the sensor.

However, according to the conventional tool breakage detection device, since the AE sensor is provided near the workpiece, the level of the AE signal varies greatly depending on the mounting position. Therefore, conventional tool breakage detection devices
The sensitivity of the AE sensor was set to a predetermined standard value depending on the size of the tool, and the attenuation rate between the tool and AE sensor of each machine tool was corrected through trial and error. However, since the AE signal when a tool breaks can only be obtained when the tool breaks, it is difficult to confirm the mounting position and mounting condition of the AE sensor, making it difficult to reliably detect tool breakage. Furthermore, the type of tools,
For example, when changing the drill diameter or cutting conditions such as rotation speed, the level of the AE signal differs for each workpiece with a different shape and material, making adjustment difficult, making it difficult to use, and causing reliability problems. There were flaws.

[Purpose of the invention]

The present invention was made in view of the problems of the conventional tool breakage detection device, and it is possible to extremely easily set the sensitivity of the AE sensor without depending on the shape, material, or surface condition of the workpiece. The purpose of the present invention is to provide an easy-to-use tool breakage detection device.

[Structure and effects of the invention]

The present invention is provided in a tool support section of a machine tool.
A tool breakage detection device that has an AE sensor and detects breakage based on an AE signal obtained when a tool breaks, and has a mounting part with a shape corresponding to the shape of the tool attached to the tool mounting position, a pseudo AE signal generating means for generating a pseudo AE signal of a predetermined level according to the type of tool, including the frequency of the AE signal obtained when the tool breaks; a display for displaying the output level of the AE sensor; Sensitivity setting means for setting sensitivity, and setting the sensitivity of the AE sensor based on the pseudo AE signal obtained when the pseudo AE signal generating means is attached to the tool attachment position. It is.

According to the present invention having such characteristics, the sensitivity of the AE sensor can be adjusted by generating a pseudo AE signal at the time of tool breakage using the pseudo AE signal generating means in advance before machining with a machine tool. At this time, pseudo AE is applied to the tool mounting part of the machine tool.
A signal generating means is provided, and an AE sensor is provided on the tool support. Therefore, if a pseudo AE signal is generated by the pseudo AE signal generating means, the pseudo AE signal is transmitted to the AE sensor through the same transmission path as the AE signal transmitted when the tool breaks. At this time, adjust the sensitivity of the AE sensor to obtain an appropriate signal. This makes it extremely easy to optimally adjust the mounting position and sensitivity of the AE sensor.

If the tool is attached after completing the adjustment in this way, if the tool breaks, the pseudo AE signal will be sent along the same path as the pseudo AE signal.
The AE signal is transmitted to the AE sensor. Therefore, it is not affected by the type, shape, surface condition, or material of the workpiece 1, nor is it affected by the attenuation of the AE signal from the tool to the AE sensor, greatly improving the reliability of tool breakage detection. This makes it possible to provide a tool breakage detection device that is easy to use.

[Explanation of Examples]

FIG. 1 is a block diagram showing an embodiment of a tool breakage detection device according to the present invention. This embodiment shows a state in which the workpiece 1 is attached to a drilling machine, and a workpiece 1 is fixed on a base 2 of the drilling machine, and a drill is attached to a drill support part 3 from above to provide an opening in the workpiece. Here, before cutting the workpiece, simulate AE at the drill mounting position of the drill support part 3.
A signal generator 4 is attached. As will be described later, the pseudo AE signal generator 4 generates a pseudo AE signal that is similar to the AE output waveform when the tool breaks and has the same power spectrum distribution. An AE sensor 5 is provided on the side surface of the drill support portion 3 as shown in the figure. The AE sensor 5 receives AE signals from tools such as drills and AE from the pseudo AE signal generator 4.
It is a wideband AE sensor that detects signals, and its output is given to the analog switch 6. The analog switch 6 connects and cuts the analog signal using an external output, and its output is applied to the amplifier 7. The amplifier 7 is an amplifier whose amplification factor can be arbitrarily set by adjusting a variable resistor 8, and its output is passed through two bandpass filters 9,
10 and the cutting level indicator 11. Bandpass filter 9 has a center frequency of 300KHz.
The bandpass filter 10 is a filter with a center frequency of 50 KHz, and transmits only signals near the respective center frequencies to the next-stage detectors 12 and 13. Detector 1
Reference numerals 2 and 13 each detect the input signal and obtain an output corresponding to the amplitude.The output of the detector 12 is applied to a differentiating circuit 14, and the outputs of the detectors 12 and 13 are applied to a comparator 15, respectively. These bandpass filters 9, 10, detectors 12, 13, and comparator 1
5 forms a frequency identification means for identifying the AE signal at the time of breakage. The differentiating circuit 14 transmits only the steep changes in the input signal to the next stage level determiner 16 and breakage/abnormal level indicator 17. The level determiner 16 compares the input signal with a predetermined reference level, and if the input signal is large, transmits the output to the breakage detection circuit 18 and the abnormal cutting detection circuit 19. Further, the comparator 15 compares the outputs of the wave detectors 12 and 13, and transmits the output to the breakage detection circuit 18 only when the output of the wave detector 12 is large. Breakage detection circuit 18
is a logic circuit which calculates the AND of these inputs to detect tool breakage, and closes the analog switch 6 based on the detection signal and outputs the signal to the outside via the output circuit 20. Also, abnormal cutting detection circuit 19
detects abnormal cutting based on the output of the level determiner 16, and outputs the output to the output circuit 21.
The information is communicated to the outside through the .

FIG. 2 is a sectional view showing an example of the pseudo AE signal generator 4, and FIG. 3 is a block diagram showing its electrical configuration. In these figures, a battery 31 is provided inside a casing 30 of the pseudo AE signal generator 4. Further, a selection switch 32 for selecting the level of the generated AE signal is provided on the side thereof, and the output of the switch and the power supply are connected to the drive circuit 3.
Added to 3. As shown in FIG. 3, the drive circuit 33 is provided with a clock generator 34 which generates a square wave clock signal at a predetermined timing, and a differentiation circuit 35 which differentiates the output thereof. The differentiating circuit 35 generates a substantially triangular waveform output, and the output is given to a multiplier 36. Further, the drive circuit 33 is provided with a noise generator 37 that generates white noise having a uniform frequency distribution, and a bandpass filter 38 that extracts only signals with a frequency of around 300 KHz from the noise output. The output and the output of the differentiating circuit 35 are connected to the multiplier 3
Multiplied by 6. By doing so, the multiplier 36 generates a pseudo
AE signal is generated. The output of the multiplier 36 is amplified by an amplifier 39 with an amplification factor selected by the level selection switch 32. The amplified output is then given to a piezoelectric element 40 attached to the upper inner surface of the case 30. The piezoelectric element 40 converts a given electrical signal into a corresponding mechanical vibration, and transmits a pseudo AE signal to the tool support of the machine tool. The upper part of the case 30 of the pseudo AE signal generator 4 is made of a metal member that easily transmits the AE signal, and the upper part is made of a cylindrical member 41 having a constant diameter corresponding to the drill diameter used.
is made to protrude upward.

FIG. 4 is a partial sectional view showing the similar AE signal generator 4 attached to the tool support. In this figure, the tool support part 3 has a main shaft 51 rotatably held by a bearing part (not shown), and a chuck 52 for attaching a drill to the tip of the main shaft 51.
is provided. Normally, a drill of a desired diameter is attached to the tip of the chuck 52, but when operating this tool breakage detection device, the above-mentioned pseudo
The upper cylindrical member 41 of the AE signal generator 4 is fixed.
It is assumed that the AE sensor 5 is attached to the side surface of the tool support section 3 as shown in the figure.

Next, the operation when installing the tool breakage detection device of this embodiment in a machine tool will be explained. First, pseudo
After attaching the AE signal generator 4 to the chuck 52, the level setting switch 32 is operated to set a pseudo AE signal level according to the type of tool used, for example, the drill diameter. After operating the pseudo AE signal generator 4, the machine tool is driven. Since the pseudo AE signal generator 4 has a battery 31 inside,
Operates without external power supply. Therefore, by rotating the main shaft 51, a pseudo AE signal can be obtained in a state close to the actual operating state of the tool.
At this time, the amplification factor is adjusted by the variable resistor 8 of the amplifier 7 that amplifies the AE signal so that the display on the cutting level indicator 11 becomes a predetermined level. By setting this for each tool used, it becomes possible to adjust the sensitivity of the AE sensor 5, that is, the output of the amplifier 7, to a constant level. At this time, pseudo
The AE signal is transmitted from the spindle 51 through the tool support 3.
The AE signal is transmitted to the sensor 5, but even when a drill is attached to the chuck 52, the AE signal is transmitted through the same transmission path when the drill breaks, so it is not affected by the shape or material of the workpiece. Therefore, when the tool breaks, a signal of the same level as the AE output of the pseudo AE signal is transmitted to the signal processing section.

Now, the distribution of the power spectrum of the AE signal given by the AE sensor 5 during normal cutting is the fifth
As shown by curve b in the figure, it is concentrated around the frequency of 50 KHz, and the distribution is monotonically attenuated in the higher frequency range. . Furthermore, as is known from many experiments, the power spectrum distribution when a tool breaks is represented by curve a in Figure 5, and the frequency
It has become clear that it has a peak around 300KHz. This is considered to be because the signal source is not caused by mechanical vibration, but a phenomenon peculiar to ultrasonic waves that occurs during non-plastic fracture of a tool occurs. Therefore, by extracting only the AE signals near the respective frequency components using the two bandpass filters 9 and 10 and detecting them using the detectors 12 and 13, and comparing the output levels, it is possible to clearly distinguish between normal conditions and tool breakage. It is possible to do so. In other words, during normal cutting, the frequency
The power of the AE signal around 50KHz is the frequency
This is because the power around 300KHz is higher than the power around 300KHz, and when the tool breaks, the power around 300KHz is higher than the power around 50KHz. The comparator 15 compares these outputs and provides a signal to the breakage detection circuit 18 only when the tool breaks.

On the other hand, a signal similar to the power spectrum distribution shown by curve a in FIG. 5 may be generated due to contact or friction between chips and the tool workpiece during cutting. In this case, bandpass filters 9, 10
Even if the center frequency and Q value of , the threshold level of the comparator 15, etc. are set appropriately, a signal caused by contact or friction between chips and a tool or workpiece may be mistakenly determined to be a tool breakage signal. Therefore, in this embodiment, attention is also paid to the time-domain waveform of the AE signal seen when the tool breaks, and these signals are separated. In other words, the AE signal waveform obtained when the tool breaks is a signal with a sharp rise as shown in Figure 6a, while the AE signal generated by contact and friction between chips and the tool or workpiece has a sharp rise. As shown in FIG. 6b, the waveform does not show a sharp rise and continues for a predetermined period of time. Therefore, the first
As shown in the block diagram, the output of the detector 12 is applied to a differentiating circuit 14, and only steep signals such as those caused by breakage are separated and applied to a level determiner 16. Then, the input level is compared with a predetermined reference value, and when an AE signal with a steep rise is obtained, the level judger 1
6 gives a signal to the breakage detection circuit 18. The breakage detection circuit 18 detects tool breakage based on these AND signals. In this way, by combining both frequency domain breakage detection and time domain breakage detection, it is possible to reliably detect only tool breakage.

In this way, if only a breakage of the tool is detected, the output circuit 19 provides a breakage output, and the analog switch 6 is turned off so that no AE signal is transmitted to the amplifier 7 thereafter. This is to prevent a large AE signal generated due to abnormal contact or friction between the broken tool and the workpiece that occurs after the tool breaks from being further determined as a breakage. In addition, as shown in the block diagram of Fig. 1, the output of the amplifier 7 is directly displayed on a cutting level indicator 11 to indicate the cutting level, and furthermore, abnormal contact friction between chips and the workpiece can be detected by tool breakage or normal cutting. It is possible to separate it as a processed signal. The output circuit 2 is outputted from the level determiner 16 via the abnormal cutting detector 19.
Since the abnormal cutting output is given to the outside from 2, it is also possible to detect abnormal cutting at the same time.

In this embodiment, the pseudo AE signal generator is provided with a level setting switch, and by setting the setting switch appropriately according to the type of tool, a pseudo AE signal at a reference level is generated. It is also possible to use a pseudo AE signal generator having a predetermined level for each type of tool.

Further, although this embodiment describes a drill breakage detection device for a drilling machine, the present invention can also be applied to other machine tools,
For example, it can be applied to various machine tools such as lathes and milling machines.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the tool breakage detection device according to the present invention, Fig. 2 is a sectional view of the pseudo AE signal generator 4 according to the present embodiment, and Fig. 3 is a block diagram showing its electrical configuration. , FIG. 4 is a side view showing the state in which the pseudo AE signal generator 4 and the AE sensor 5 are attached to the machine tool, and FIG. 5 is a diagram showing the power spectrum of the AE signal obtained from the AE sensor 5.
Figure 6a shows the AE signal waveform obtained when the tool breaks.
FIG. 6b is a diagram showing an AE signal waveform obtained when chips are generated. DESCRIPTION OF SYMBOLS 1... Workpiece, 2... Drill, 3... Tool support part, 4... Pseudo AE signal generator, 5... AE sensor, 7... Analog switch, 7... Amplifier,
9, 10...Band pass filter, 12, 13...
...Detector, 14...Differential circuit, 15...Comparator,
16...Level judger, 18...Breakage detection circuit,
20, 21... Output circuit, 30... Case, 31
...Battery, 32...Level setting switch,
33... Drive circuit, 40... Piezoelectric element.

Claims (1)

[Scope of Claims] 1. A tool breakage detection device that has an AE sensor provided on a tool support of a machine tool and detects breakage based on an AE signal obtained when a tool breaks, which is installed at a tool mounting position. a pseudo AE signal generating means, which has a mounting portion having a shape corresponding to the shape of the tool to be broken, and generates a pseudo AE signal of a predetermined level according to the type of the tool, including the frequency of the AE signal obtained when the tool breaks; A display device for displaying the output level of the AE sensor, and a sensitivity setting means for setting the sensitivity of the AE sensor, and a pseudo AE signal obtained when the pseudo AE signal generating means is installed at a tool mounting position. Based on the signal
A tool breakage detection device characterized by setting the sensitivity of an AE sensor. 2. Claim 1, wherein the pseudo AE signal generating means has an internal power supply and generates a pseudo AE signal when the machine tool is driven.
The tool breakage detection device described in section. 3. The tool breakage detection device according to claim 1, wherein the pseudo AE signal generating means includes level setting means for setting an AE signal level according to the type of tool.